1. Field of the Invention
The invention relates to a vehicle, and more particularly, to an attitude control of a vehicle using an attitude control of an inverted pendulum.
2. Description of the Related Art
A vehicle which allows a driver to be seated on drive wheels aligned on a shaft and travels while maintaining the balance like a unicycle with the attitude control of the inverted pendulum (hereinafter referred to simply as an inverted pendulum vehicle) has been focused and put to the practical use.
Japanese Patent Application Publication No. JP-A-2004-276727 proposes the technology for detecting the attitude of the drive wheel resulting from the movement of the gravity center of the driver so as to drive the vehicle having two coaxially arranged drive wheels.
Japanese Patent Application Publication No. JP-A-2004-129435 proposes the vehicle which travels while controlling the attitude of a single drive wheel with circular shape or the spherical shape.
The vehicle using the attitude control of the inverted pendulum is structured to generate the driving force in accordance with the amount of movement of the gravity center of the driver or the operation amount of the remote controller so as to travel while executing the attitude control.
The above-described patent document discloses the technology which employs the weight and the counter weight (hereinafter simply referred to as the balancer) for maintaining the balance by moving the gravity center of the vehicle, which may be moved to displace the gravity center.
As Japanese Patent Application Publication No. JP-A-2005-094898 discloses, the inverted pendulum vehicle maintains the balance using principle of the wheeled inverted pendulum.
In the inverted pendulum vehicle, as the gravity center is above the axle, it is important to maintain the balance. The balance may be maintained by moving the vehicle in the direction where the gravity center moves (the direction where the vehicle tilts). However, it is effective to add the balancer for maintaining the balance.
Japanese Patent Application Publication No. JP-A-2004-129435 proposes the inverted pendulum vehicle equipped with the balancer which assists the balance maintenance.
The above proposed technology is of the balance type having the drive wheel formed as a spherical shape, the principles of which are shown in FIG. 22.
Assuming that a vehicle 100 includes a drive wheel 11, a seat unit 13 and a balancer 101 having an axle in the direction vertical to the traveling direction as shown in the drawing, when the seat unit 13 tilts, the balancer 101 is moved in the direction opposite the tilt so as to maintain the balance.
If the attitude control is executed using the aforementioned balancer 101, such technology as the attitude control using the reaction force (reaction torque) caused by accelerating the balancer 101 may be considered (not as the known technology).
Referring to FIG. 28, the control uses the torque (reaction torque) for turning the seat unit 13 in the direction opposite the direction of the balancer 101 which rotates (tilts) around the axle.
In the aforementioned process, when the external force acts on the seat unit 13 to be tilted forward, the balancer 101 is turned in the direction where the seat unit is tilted such that the attitude is controlled by allowing the torque in the direction opposite the rotating direction of the balancer, that is, the torque in the direction opposite the tilting direction of the external force to act on the seat unit.
Assuming that the seat unit 13 is tilted forward at the angle in excess of the target value, it may be restored by rotating the balancer 101 in the direction opposite the one for restoring the seat unit 13, that is, in the direction to tilt forward such that the seat unit 13 moves toward the restoring direction by the reaction torque generated upon acceleration of the balancer 101.
Referring to FIG. 28, assuming that the balancer 101 is accelerated in the direction of an arrow B, the resultant reaction torque moves the seat unit 13 in the direction of an arrow A.
According to Japanese Patent Application Publication Nos. JP-A-2004-276727 and JP-A-2004-129435, the balancer is moved in the direction opposite the direction where the gravity center of the vehicle moves.
When the balancer is moved, the reaction force in the direction opposite the movement direction acts on the vehicle. As a result, the gravity center of the vehicle (except the gravity center of the balancer) is moved in the direction opposite the one of the balancer.
In the case where the gravity center of the vehicle except the gravity center of the balancer is moved forward, and the balancer is moved backward, the vehicle gravity center is further moved forward by the reaction force, thus failing to take a balance.
The vehicle gravity center and the balancer gravity center as disclosed in the aforementioned patent documents are intended to represent the balance state in which the overall gravity center derived from combining both gravity centers locates on the plumb line of the axle, in other words, the gravity center in the stationary stable state. The aforementioned stationary stable state cannot be realized even if the balancer is moved in the direction opposite the one of the movement of the vehicle gravity center.
In the case where the attitude control is executed by moving the balancer within the limited stroke as the balancer 101 in FIG. 22, the mass of the balancer is required to be increased to a certain degree for obtaining the effect of the balancer.
The weight of the balancer system is also increased for maintaining the strength of the system, thus interfering with the improvement in the fuel efficiency.
When the balancer which is asymmetrical to the axle is rotated around the axle, the vehicle gravity center moves, thus causing the attitude control complicated.
As the balancer is operated above the axle, the space for operating the balancer is required.
As the seating position is required to be above the balancer, the vehicle height is increased, thus enlarging the entire vehicle size.
For the purpose of maintaining the balancer against the gravitational force, the resultant energy consumption is increased.
In the vehicle shown in FIG. 28, the attitude control of the seat unit 13 may be executed with the reaction torque generated by accelerating the balancer 101. However, as the balancer 101 and the seat unit 13 move, the gravity center of the entire vehicle moves.
As the amount for moving the balancer 101 is determined in accordance with the amount required to move the seat unit 13, the overall gravity center of the vehicle cannot be directly controlled.
When the overall gravity center of the vehicle moves as the balancer 101 is driven, the attitude control of the vehicle becomes complicated.